Absorption and fluorescent dyes, such as indocyanine green, have proven useful for medical imaging applications. Some of the more commonly used dyes share a number of useful characteristics. First, the dyes are suitable for labeling antibodies or low-molecular-weight ligands of diagnostic significance, or otherwise adapted for sequestration or preferential uptake at a site of interest such as a lesion. The dyes are safe for injection or other introduction into a live subject. And finally, the dyes emit light at a specific wavelength when excited, so that their location and concentration may be tracked.
A number of imaging systems have been devised to detect and display these dyes within living tissue. For example, dyes such as indocyanine green have been used to visualize blood flow in eyes. In some cases, such as U.S. Pat. No. 6,293,911 to Imaizumi et al., a dye imaging device has been combined with a visible light imaging system. Imaizumi describes endoscopic tools that generate images of dye-labeled antibodies superimposed over visible light images captured from within the body. As a significant disadvantage, the Imaizumi system employs a number of separate cavities within an endoscopic tool for light sources and image capture, thus requiring a greater cross-sectional area for the endoscope. As a further disadvantage, the Imaizumi patent only discloses endoscopic applications, and may not be suitable for use in open surgical applications where ambient light may extend into the excitation and/or emission wavelengths of the dye.
There remains a need for improved surgical and diagnostic imaging tools capable of generating circulatory blood flow images or other functional images along with visible light images of a subject.